Apparatus and method for obtaining undisturbed soil core samples

ABSTRACT

Large-diameter, undisturbed soil core samples were obtained from a variety of soils. Handling and fracturing of the undisturbed soil cores were minimized by encasing the cores in heatshrinkable plastic tubes during sampling operations.

ilnited States Patent Mielke 1 APPARATUS AND METHOD FOR OBTAININGUNDISTURBED SOIL CORE SAMPLES [75] Inventor: Lloyd N. Mielke, Lincoln,Nebr.

[73] Assignee: The United States of America as represented by theSecretary of Agriculture, Washington, DC.

22 Filed: Apr. 30, 1974 21 Appl. No.: 465,650

[52] US. Cl. 175/58, 175/20 [51] Int. Cl. E2lb 49/02 [58] Field ofSearch 175/58, 20, 19,253, 239

[56] References Cited 7 UNITED STATES PATENTS 3,092,192 6/1963 Deely175/253 Primaryfixaminer-David H. Brown Attorney, Agent, or Firms-M.Howard Silverstein; Max D. Hensley; David G. McConnell [s71 ABSTRACTLarge-diameter, undisturbed soil] core samples were obtained from avariety of soils. Handling and featuring of the undisturbed soil coreswere minimized by encasing the cores in heat-shrinkable plastic tubesduring sampling operations.

1 Claim, 5 Drawing Figures BACKGROUND OF THE INVENTION This inventionrelates to an apparatus and a method for obtaining undisturbed soilcores. Soil cores with undisturbed structure are desirable to measurephysical and chemical properties, particularly water content andnutrient movement.

Undisturbed soil sampling techniques using handdriven equipment werereported by Lutz, Soil Sci. 64: 399-401, 1947; and Veihmeyer, Soil Sci.27: 147-152, 1929. The machine built by Kelly et al., Soil Sci. Soc.Amer. Proc. 12: 85-87, 1947, could take undisturbed soil cores of andlO-cm. (2- and 4-in.) diameters and up to 1.8 m. (6 ft.) long. Anearlier machine reported by Kelley and Haise, J. Amer. Soc. Agron. 39:828-830, 1947, had similar sampling capabilities but required aconsiderable amount of manual labor. Hydraulic and electric unitsdeveloped to increase sampling speed have been developed by Jensen etal., Trans. Amer. Soc. Agr. Eng. 3(1): 22-24, 1960; and Buchele, Trans.Amer. Soc. Agr. Eng. 4(2): 185-187, 1961.

Kelley et al. (supra) reported using a split-sheet metal container toprotect the soil sample from fracture during transport to thelaboratory. Care in sample handling and processing is required for allundisturbed samples. Split-tube-type samplers require that the sample beremoved, trimmed, and coated with a casing material. Adsorption ofpaint-on, or dip-type coating materials, may affect the effectivecross-section of the core and provide little mechanical support. Rigidwall sample containers may permit undetected water flow paths whichwould affect results and conclusions.

Bondurant et a1., Soil Sci. 107: 70-71, 1969, used 2 tip) is up to 4 ft.long and up to about 4 in. in inside diameter. It can be a single pieceor it can have a removable cutting head. FIG. 1 is a perspective view ofa twopiece sampler tube with sampler body 1 connected to cutting tip 2which is beveled to give it the desired sharpness. FIG 2 is a sectionview of the soil sampler ready for use, taken along section-line 2-2 ofFIG. 1

showing a heat-shrinkable plastic lining 3 and a comheat-shrinkabletubing (polyolefin) to encase undisturbed soil cores. The space betweenthe soil core and the outer barrier was effectively sealed on soil cores240 mm. long and 82 mm. diameter.

In accordance with the invention, I have discovered, in an apparatus forcollecting undisturbed soil core samples of the type comprising acylindrical tube or sample body, open at both ends, and having at oneend thereof a cutting tip which is sharpened to facilitate entry intothe ground, an improvement comprising a tubular lining or flexibleheat-shrinkable plastic open'at both ends, contained within said samplerbody, and having flI'IOUISldB diameter which is essentially equal to theinside diameter of said sampler body; and a means for securely holdingsaid tubular lining in place.

This heat-shrinkable, plastic-lined soil core sampler is then pressedinto the ground, removed from the ground, and the plastic lining heatedto a temperature sufficient to cause shrinkage of the plastic to thesoil.

The drawings consist of a perspective view and two section views of thesampler body, and two perspective views of retaining rings.

DETAILED DESCRIPTION OF THE INVENTION Many commercially available soilcore samplers could be easily modified for use in accordance with theinvention. Preferably, the sampler is a thin-walled metal tube with asharpened cutting tip at one end. Its size is dependent on the type ofsoil being sampled. Preferably, the entire soil core sampler (i.e., bodyplus pressible, resiliant retaining ring 4 in place. Retaining ring 4 ispositioned in an annular groove 5 in the inner wall of sampler body 1.FIG. 3 shows the same section view as FIG. 2 with the exception thatannular groove 5 is internal of threaded section 6 on sampler body 2Having threads in the annular groove 5 in the embodiment of FIG. 2provides a gripping surface for the heatshrinkable plastic lining. It ispreferred that this or some other type of gripping surface be provided.

The heat-shrinkable plastic lining can be securely held in place by anysuitable means, but it is preferably held in place by a compressible,resiliant retaining ring 4,4 such as that shown in section in FIGS. 2and 3 and in perspective in FIGS. 4 and 5.. The preferred compressible,resiliant retaining ring is beveled on the leading inside edge 7 asshown in FIG. 3. This bevel prevents undercutting the soil core as itpasses through the retaining ring. It is also preferred that thecompressible, resiliant retaining ring be split to facilitatecompression of the ring in order to fit it into annular groove 5,5 inthe inner wall of the sampler body, and that the retaining ring ends 8,8in FIGS. 2, 3, 4., and 5 be notched in such a manner that when the ringis in place in annular groove 5,5 the ends will maintain alignment withrespect to each other. The compressible, resiliant retaining ring 4,4and annular groove 5,5 must have dimensions such that, when theheat-shrinkable plastic lining 3,3 and the compressible, resiliantretaining ring 4,4 are in place, the lining will be held with sufficientsecurity to withstand the forces of friction of the soil core whenpushing the soil core sampler into the ground. This was accomplished inone embodiment of the invention, as shown in the figures, by using aretaining ring 4 'such that, when the retaining ring is compressed, itsoutside diameter is essentially the same as the diameter of the annulargroove 5. When the outside diameter of the compressed retaining ring andthe diameter of the annular groove are said to be essentially the same,it is herein understood that the diameter of the annular groove issufficiently larger than the outside diameter of the compressedretaining ring to allow the retaining ring to be put in place with theheatshrinkable plastic lining in between the retaining ring and thesurface of the annular groove (cf. FIGS. 2 and 3). The edges of theretaining ring may be of different dimensions so that the outer surfaceof the ring is beveled as shown in FIG. 5. In this instance annulargroove 5 should be beveled in the same manner as the ring as shown inFIG. 2.

Compressible, resiliant retaining rings suitable for use in theinvention may be of any material that is rigid, and has sufficientspring to hold itself and the heatshrinkable plastic lining in place. Inthe embodiment shown in FIGS. 2 and 3 removable cutting tip 2,2 isscrewed into sampler body 1,1 forcing the tip against retaining ring 4,4in such a way that the ring is held tightly in place. However, aretainingring could be used that has enough force to its *spring" thatthe he atshrinkable plastic lining would be held securely in an annulargroove that was positioned by itselfin the inner wall of the samplerbody. In thisembodiment a onepiece sampler body and cutting tip could beused. Methods of securing a removable cutting tip to the sampler bodyother than threads could be used, such as a bayonet-type mounting.

Commercially available heat-shrinkable plastic tubing have variouscompositions including tetrafluoroethylene resins (TFE or FTE),polyolefins, and irradiated polyvinyl chloride (PVC). These products areavailable in continuous rolls and 4-ft. lengths with diameters of up to8 in. and in various colors or clear plastic. The tubing remainsflexible after being heatshrunk and does not soften, when heated, to thepoint where soil particles might become embedded. Clear, heat-shrinkableplastic tubing is preferred to permit observation of wetting fronts andother conditions such as growth of microorganisms during the measurementof physical and chemical properties of the soil. Shrinking of theplastic is accomplished by subjecting it to temperatures of about 135 C.For optimum results the heat should be applied as evenly as possibleover the surface of the encased core.'Suffic ient heat can be applied tothe encased core while in the soil core sampler, or the encased core canbe removed from the sampler before heating.

In use, the soil core sampler with the heat-shrinkable plastic liningsecurely in place is pushed into the ground to the desired depth byhydraulic pressure or similar means. Preferably, the sampler is forcedinto the soil at a constant rate without stopping until the desireddepth is reached. The sampler is then pulled out of the ground, and theheat-shrinkable plastic is heated, encasing the soil sample. Means forforcing the sampler into the ground and removing it from the ground arewell known in the prior art.

The following example is to further describe the invention and shouldnot be construed as limiting the scope of the invention as defined bythe claims.

EXAMPLE 1 White heat-shrinkable FTE tubing 4 in. in diameter and 4 ft.long was shaped to the inside contours of a 4-in. inside diameter, 4-ft.overall length soil core sampler having a threadmounted, removablecutting tip as shown in FIG. 3. A l6-gauge, compressible, resiliantretaining ring of the type shown in FIG. 4 was compressed to itssmallest diameter and slipped into place on one end of theheat-shrinkable plastic lining at the edge of the sampler body threadswhich hold the cutting tip. The cutting tip was then screwed on, forcingthe retaining ring against the inner surface of the sampler body (seeFIG. 3).

The heat-shrinkable, plastic-lined soil core sampler described above wasforced into the ground of a beef cattle feedlot with a Gidding,truck-mounted hydraulic probe, model GSRP-ST equipped with a Kelly bar 5(driven bar). The sampler was forced into the soil at a constant ratewithout stopping until a depth of about 4 ft. was reached. The soil coresampler was retracted from the soil, the cutting tip unscrewed, and the.retaining ring removed. The soil core encased in heatshrinkable plasticwas removed from the sampler and supported on a flat surface. End plugsabout the same size as the sample core were placed in each end of theplastic tube to help shape and protect the soil core when theheat-shrinkable plastic is heated and shrunk. Heat was uniformly appliedto the plastic from a portable blower having a 400 to 538C. heat outputand a 0.25 m. per minute air output until the shrinkage was uniform.

Six undisturbed cores from to 35 in. long were successfully removed fromfeedlots underlain with sandy and silty-loam soil, and one undisturbedcore 37 in. long was successfully removed from a cropped cornfield.

The undisturbed soil cores were used with gamma ray attenuationtechniques as a nondestructive method of investigating water movementunder beef cattle feedlots. Initial observations indicated that watermovement into feedlot surfaces is very slow. Water applied to thesurface of one undisturbed core showed no further infiltration over a2l-da. period following initial adsorption by the relatively dry organicmatter. While this represents an extreme soil and water condition, itshows that an effective seal exists between the soil column and theheat-shrinkable tube.

I claim:

1. In a method of obtaining undisturbed soil core samples of the typewhich utilizes a soil core sampler comprising a cylindrical tube orsampler body, open at both ends, and having at one end thereof a cuttingtip which is sharpened for facilitating entry into the soil, animprovement comprising the steps of:

a. lining the inside surface of a soil core sampler with a flexibleheat-shrinkable plastic tube; b. securing said heat-shrinkable plastictube to the inner wall near the cutting tip end of said soil coresampler;

c. pressing the lined soil core sampler into the ground;

d. removing the soil sampler from the ground; and

e. heating said heat-shrinkable plastic tube evenly on all sides at atemperature sufficient to cause shrinkage.

1. In a method of obtaining undisturbed soil core samples of the typewhich utilizes a soil core sampler comprising a cylindrical tube orsampler body, open at both ends, and having at one end thereof a cuttingtip which is sharpened for facilitating entry into the soil, animprovement comprising the steps of: a. lining the inside surface of asoil core sampler with a flexible heat-shrinkable plastic tube; b.securing said heat-shrinkable plastic tube to the inner wall near thecutting tip end of said soil core sampler; c. pressing the lined soilcore sampler into the ground; d. removing the soil sampler from theground; and e. heating said heat-shrinkable plastic tube evenly on allsides at a temperature sufficient to cause shrinkage.